The objective of the proposed research is to develop an understanding of the structure and physiochemical characteristics of molecules which influence the probability that the molecules will undergo bioactivation by mammalian arylhydroxamic acid acyltransferase(s). The objective will be accomplished by quantitatively evaluating the influence of substituents of varying chemical and physical properties upon the ability of arylhydroxamic acids to function as acyl donors in the acyltransferase reaction in vitro; substituted N-hydroxy-2-acetylaminofluorenes (N-hydroxy-2-fluorenylacetamides) and substituted N-hydroxy-trans-4-acetylaminostilbenes (N-hydroxy-trans-4-stilbenylacetamides) will be used as the model substrates. Partially purified hepatic arylhydroxamic acid acyltransferase from rats and hamsters will be used in these studies and enzyme activity will be monitored by spectrophotometric measurement of acyl group transfer to p-phenylazoaniline (4-aminoazobenzene) and by the use of N-acetylmethionine as a trapping agent for the activated intermediates.